106 GENERAL EVOLUTION. 



Similar analogies have been pointed out by Bates among the 

 Lepidoptera of Brazil, and by Wallace among those of Borneo 

 and Celebes, etc. I call attention to these authors here without 

 cojDying them, as they will rej^ay perusal in the originals. 



A case of analogy which may belong to this class is that of the 

 three genera Chelys among tortoises^ Pipa among frogs, and As- 

 predo among Siluroid fishes, species of which inhabit at the same 

 time the rivers of Guiana. The crania of these genera are simi- 

 larly excessively flattened and furnished with dermal appendages, 

 and their eyes are very minute. The singular similarity need only 

 be mentioned to those familiar with these genera, to be recognized. 



The bearing of the mimetic analogy, on the question of transi- 

 tion of types in the developmental hypothesis, is its demonstra- 

 tion of the independence of generic and specific characters of each 

 other, which may suggest the possibility of the former being 

 modified without affecting the latter. 



These facts might have been introduced under Section II a, but 

 •they illustrate the general laws of the present section. 



IV. OF NATUEAL SELECTION". 



a. As affecting Class and Ordinal Characters. 



The second law which may be supposed to have governed a 

 descent with modification, in the production of existing genera, 

 is the force which the environment exercises in permitting or for- 

 bidding the existence or persistence of new forms. The forms 

 which survive are supposed to have done so by virtue of their su- 

 perior adaptation to their environment. This is the " natural 

 selection " of Darwin. 



That this law is subordinate to the one first propounded must, 

 I think, be evident to any one who studies the assumed results of 

 the workings of both, as seen in the characters of genera. It is 

 sufficiently well known that the essential features of a majority of 

 genera are not adaptive in their natures, and that those of many 

 others are so slightly so, as to offer little ground for the suj)posi- 

 tion that this necessity has preserved them. 



Both laws must be subordinate to that unknown force which 

 determines the direction of the great series. If a series of sup- 

 pressions of the nervous and circulatory systems of beings of com- 

 mon birth produced the " synthetic " predecessors of the classes 

 of Vertebrata, the direction toward which the highest advanced, 



